Arrangements of this type are described, for instance, in German Utility Pat. No. DE-GM 73 18 689 for the air outlets of air conditioning systems. In such arrangements, the effectiveness of the air deflecting louvers is somewhat limited inasmuch as the air traveling through the portion of the nozzle between the outermost louvers and the nozzle wall is either not deflected at all, or is deflected only to a limited extent, into the direction corresponding to the pivoting position of the air deflecting blades, with the result that non-directed marginal air currents are created. This, in turn, causes the air currents between two respective air deflecting blades to be partially redirected from the desired flow path.
In German Auslegesschrift No. DE-AS 21 14 297, the air deflecting blades are in the form of stationary elements that are arranged inside barrel-shaped rotatable bodies, and these rotatable bodies are accommodated in respective chambers that form the air discharge nozzles. The rotatable bodies can be adjusted so as to assume various pivoting positions enabling the air exiting from the discharge nozzle to be deflected into the desired direction. Furthermore, pairs comprised of two adjacent air deflecting blades are arranged inside the rotatable body so as to form a funnel-like patterns, the arrangement being such that each such pair of blades forms an air duct in which the cross-sectional area of the duct diminishes from one end to the other end of the duct. Accordingly, the cross-sectional areas of the inlet and outlet openings of the rotational body differ in size. This arrangement enables production at the outlet of the nozzle of converging or diverging air currents, depending on whether the smaller or larger cross-sectional area is disposed on the outlet end. Furthermore, the arrangement is such that large pivoting movements of the rotational body change the pattern of the air currents exiting from the discharge nozzle, whereas smaller pivoting movements only cause the air currents to change direction.
In this prior art arrangement, no non-directed marginal air currents are produced because the passages through which the lateral air currents are directed are defined, respectively, by one air deflecting blade and one wall portion of the rotatable body, so that when the rotatable body is moved into a different position, the pivoting movement of the wall portion of the rotatable body is the same as that of the air deflecting blade. However, in comparison to discharge nozzles with individually pivotable air deflecting blades, as described earlier, this arrangement requires a considerably larger volume of space if air currents of large cross-sectional areas are to be controlled.